Journalists and bloggers are among several groups that have been harassed and threatened by authorities in the Russian city of Sochi in the build-up to next year's Winter Olympics, reports Human Rights Watch (HRW).

Two journalists and a newspaper director are said to be facing criminal charges after reporting stories viewed by local authorities as negative.

Some journalists told HRW that the authorities are seeking to control information about the preparations for the Sochi games by pressuring editors to present them in a positive light.

In addition, several independent online news sources and blogs that have posted critical stories or comments about the Olympics have had their sites disabled by hackers.

"Press freedom is a central tenet of the Olympic charter and no successful games can take place in an atmosphere in which journalists are afraid to report on stories of legitimate public interest," said HRW's Jane Buchanan.

She added that the International Olympic Committee "should insist that the Russian authorities guarantee full media freedom for each and every journalist reporting in, or travelling to, Sochi."

HRW says it has also documented government efforts to intimidate several organisations and individuals who have spoken out against the abuse of migrant workers during the building of venues, or shown concern about the environmental impact of the construction.